Singleton that gives easy access to the active [UserManager]. Singleton that gives easy access to the active [UserManager]. A [UserManager] can register itself as the active manager. If this happens all methods in this class will call the respective method in that [UserManager]. Create a [User] using the active [UserManager]. Returns all [User]s. Returns the [User] which have the given id or null if it doens't exists. Returns the [User] which have the given email or null if it doens't exists. Returns the active [UserManager]. Returns the [User] which have the given user_name or null if it doens't exists. Returns whether an email is taken or not. Returns whether a user name is taken or not. Save the [User] using the active [UserManager].